Use this Cash ISA calculator to estimate how your tax-free savings could grow over time and
whether your contributions fit current ISA limits.
Estimated balance
£0
Based on your planned contributions, interest rate, and time period
Cash ISA projection
Total interest earned
£0
Your contributions
£0
Annual ISA usage
£0
Ruleset
-
Cash ISA balance over time
Yearly breakdown
Year
Age
Contributions
Interest earned
Closing balance
Assumptions
Estimates assume a fixed interest rate over the full period and current or planned ISA rules
for the selected ruleset.
This version does not include provider fees, inflation, ISA transfers, or flexible-ISA
replacement behaviour.
How a Cash ISA works
A Cash ISA is a savings account wrapper where interest is tax free. Instead of calculating
savings tax each year, your main planning question is usually how quickly the balance could
grow and whether your planned contributions stay within annual ISA limits.
This calculator focuses on that planning task: growth over time, deposits versus interest,
and allowance checks for the selected ruleset.
Cash ISA vs normal savings account
A normal savings account may generate taxable interest once you exceed your available tax-free
savings allowances. A Cash ISA keeps interest tax free inside the ISA wrapper, so this page
focuses on growth and contribution limits instead of savings tax calculations.
If you want to estimate tax outside an ISA, use our Personal Savings Allowance calculator
alongside this one.
Current ISA limits explained
The overall ISA subscription limit for the 2026/27 tax year is £20,000. In the 2026/27 mode
on this page, that overall limit is the allowance check used for planned contributions.
This calculator shows allowance warnings instead of blocking results, so you can still model
growth even when your contribution plan would exceed a limit.
Planned Cash ISA cap changes from 2027
This calculator includes a planned 2027/28 ruleset starting from 6 April 2027. In that mode,
the overall ISA limit is still modelled as £20,000, while the cash ISA cap is modelled as
£12,000 for under-65s and £20,000 for people aged 65 and over.
This gives you a simple way to compare today's planning assumptions with the planned
ruleset without adding detailed tax-year split complexity.
What a flexible Cash ISA is
Flexible Cash ISAs can allow money withdrawn and replaced in the same tax year without using
extra ISA allowance, depending on provider terms. This version does not model detailed
withdrawal timing or replacement behaviour.
Treat these results as a practical growth and allowance planning guide under fixed-rate
assumptions.
Frequently Asked Questions
For the 2026/27 tax year, the overall annual ISA allowance is £20,000. This calculator
also supports a planned 2027/28 ruleset where the cash ISA cap is £12,000 for under-65s
and £20,000 for age 65 and over.
Yes. Interest earned within a Cash ISA is tax free under current ISA wrapper rules.
The overall ISA subscription limit in the 2026/27 tax year is £20,000.
In this calculator, the 2026/27 ruleset checks only the overall £20,000 ISA allowance.
The 2027/28 planned ruleset applies a cash ISA cap of £12,000 for under-65s and £20,000
for age 65+.
A flexible ISA can let you replace money you withdrew in the same tax year without using
extra ISA allowance, subject to provider rules.
More UK Financial Calculators
Want to compare tax-free Cash ISA growth with ordinary savings? See our interest calculator.
Saving for a target amount? Try our savings goal calculator. Saving for a first-home deposit?
See our Lifetime ISA calculator. Saving for a child? Try our Junior ISA calculator. Want to
check tax on savings outside an ISA? Use our Personal Savings Allowance calculator. Want to
plan for future buying-power loss as well? Try our Inflation Impact Calculator.